I. Technical Field
The present invention relates to a seal structure between tail ducts of a plurality of combustors which are arranged in the circumferential direction of a gas turbine, in the connection between the outlet ends of the tail ducts and an inlet nozzle of the gas turbine, and in particular to a simple seal structure for sealing between opposed surfaces of adjacent flanges of the outlet ends of the tail ducts in order to prevent compressed air on the high pressure side from entering into a combustion gas passage.
II. Description of Related Art
Referring to FIG. 17 which is a sectional view illustrating a commonly known configuration of a premix combustion type gas turbine combustor, a gas turbine 01 is mainly composed of a compressor 02, gas turbine combustors 03 and a gas turbine 04. The combustors 03 are installed in a wheel compartment 05 having a hollow space defined between the compressor 03 and the turbine 04, each being composed of an inner duct 06 defining therein a combustion zone, a tail duct 07 coupled to the front end of the inner duct 06, an outer duct 08 arranged, concentric with the inner duct 06, a pilot nozzle 09 extended from the rear end of the inner duct 06 on the axial line of the inner duct, a plurality of main nozzles 010 arranged around the pilot nozzle 09 at equal circumferential intervals, a bypass duct 011 coupled to a side wall of the bypass duct 07 and opened to the wheel compartment 05, a bypass valve 012 connected in the bypass duct 011, and a bypass valve changing mechanism 013 for adjusting the opening degree of the bypass valve 012.
In the above-mentioned configuration, the compressed air compressed in the compressor 02 flows into the wheel compartment 05 (as indicated by a void arrow in the figure), then is turned by an angle of about 180 deg. (as indicated by the solid line arrow in the figure) after passing through an annular space defined between the outer peripheral surface of the inner duct 06 and the inner peripheral surface of the outer duct 08, and is finally led into the inner duct 06 at the rear end of the latter. Next, the compressed air is mixed with fuel injected from a pilot burner (which is not shown) so as to carry out premixed combustion, and accordingly, a high pressure and high temperature combustion gas is produced. The thus produced combustion gas is led through the tail duct 07 so as to be discharged from the outlet end of the latter in order to drive the turbine 04. It is noted that a part of the compressed air is fed into the tail duct 07 and the like from the wheel compartment 05 by way of the bypass duct 011 in order to regulate the density of the combustion gas.
Further, there are shown a flange part 019 connecting between the combustion gas outlet end of the tail duct 07 and a turbine nozzle part 018, first stage rotor blades 016 attached to a turbine main shaft 015, first stage stator vanes 017A provided just downstream of the turbine nozzle part 018 and second stage stator vanes 017B. The compressed gas flows through a space surrounding the outer periphery of the flange part 019 at a pressure higher than the combustion gas passing through the inside of the flange part 019, and accordingly, sealing is required in order to prevent the compressed gas from entering into the inside of the flange part 019.
For example, Japanese Patent Laid-Open No. 2000-257862 discloses a seal structure for the outlet flange part 019 of the tail duct of the gas turbine combustor. This seal structure is used for sealing the inner edge side and the outer edge side of opposed parts of the outlet end of the tail duct of the gas turbine combustor and the turbine inlet nozzle, and is adapted to prevent a seal part from being worn due to thermal explanation of flanges provided to the opposed parts so as to prevent deterioration of a sealing function by providing an air passage for introducing cooling air (compressed air) into a combustion gas passage, in the seal part.
Further, Japanese Patent Laid-Open No. 2002-339706 (JP '706) discloses a seal structure between opposed parts of the outlet end parts of the tail duct of a gas turbine combustor and a turbine inlet nozzle or a seal structure between adjacent tail ducts, in which a planar seal assembly composed of a textile-like or nit-like metal fabric and a sheet-like nonporous high-temperature resistant metal shim arranged on the high pressure side of the metal fabric, is inserted in a slot formed in a seal part in order to enhance the seal performance.
FIG. 18A to FIG. 18C show the seal structure of the outlet end part of the tail duct. That is, FIG. 18A is an explanatory view illustrating the seal structure as viewed from the turbine nozzle side, FIG. 18B is a view illustrating the seal structure as viewed in the direction of the arrows b in FIG. 18A, and FIG. 18C is an enlarged view illustrating a part c in FIG. 18B. A plurality of combustors are arranged in the number from 16 to 18, circumferentially around the gas turbine body, and there are shown outlet end parts 07 of the tail ducts of the combustors, flanges 019 provided at the outlet end parts of the tail ducts, for connection to a turbine nozzle part 018, combustion gas passages g extended from the tail ducts 07 to the turbine nozzle part 018, and compressed air passages a defined between the adjacent tail ducts 07 within the wheel chamber 05.
The seal structure between the outlet end parts 07 of each adjacent tail ducts has such a configuration that a planar seal assembly 023 disclosed in JP '706 is inserted in recess grooves 24, 25 which are formed spanning between opposed surfaces t1, t2 of the outlet flanges 19 in order to seal between the flanges 019 of the tail ducts. It is noted that as shown in FIG. 18A, the seal assembly 023 has a handle 023a for gripping the seal assembly 023 during the handling of the seal assembly 023.
The tail duct part of the gas turbine combustor is presented in a high temperature atmosphere, and accordingly, a seal member itself requires a certain degree of rigidity in order to hold its effective sealing function under the high temperature atmosphere. However, with this high rigid seal member, it is likely to cause a slight gap between a flange of an equipment and a seal surface.
Further, due to a thermal deformation, relative displacements in all directions, that is, a circumferential direction, a radial direction and an axial direction occur. However, there has not yet been found a heat resistant and low rigid seal member which can follow up the above-mentioned relative displacements.
Further, due to vibration, the seal member is lifted up from the associated seal surface, resulting in occurrence of problems, that is, an inferior sealing effect, abrasion of the seal surface, an aging effect such as deterioration of the seal surface caused by contact therewith due to long time use, gradual increase of leakage at the seal surface and the like.
In particular, opposed surfaces of the flanges of the adjacent tail ducts are subjected to a remarkable relative displacement in the axial direction of the tail duct (in the direction indicated by the arrow b shown in FIG. 19), being caused by thermal deformation and vibration. As shown in FIG. 19, the opposed surfaces t1, t2 of the two flanges 021, 022 of the adjacent tail ducts remarkably cause a relative displacement Δδ in the axial direction b of the tail duct, due to thermal deformation, and since the combustion gas g around the outlets of the tail ducts has a pressure which is lower than that of the compressed air a in the wheel compartment arranged outside of the tail ducts by a value corresponding to a pressure loss, and accordingly, due to the pressure difference therebetween, the conventional seal member 023 is pressed against the inner surfaces 024a, 025a, on the combustion gas passage side, of recess grooves 024, 025 which are formed spanning between the opposed surfaces t1, t2.
In this case, the conventional seal member 023 would cause a gap between itself and the seal surface 025a due to the relative displacement Δδ, resulting in occurrence of leakage r.
It is noted that, in the case of occurrence of the leakage between the tail ducts of the combustors, the compressed air a in the wheel compartment 05 arranged outside of the tail ducts is mingled with the combustion gas g flowing through the tail ducts so as to increase the air mixing ratio, resulting in a temperature rise, and accordingly, there would be caused problems of an increase in emission of NOx, deterioration of combustion efficiency, and the like.